There aren't many details revealed in the FCC filing, but it does show that the controller would have Bluetooth to wirelessly connect to the Switch. From looking at the image, the controller may have ZL and ZR buttons on the top or it could be a Joy-Con docking rail.
This wouldn't be the first time Nintendo has released a retro controller for the Switch. Last year, the company announced it would make wireless NES controllers for the console, but in our opinion they were too pricey for what they offered. The company also released a range of classic NES titles for the Switch like Super Mario Bros. 2 and Kirby's Adventure.
As well as the potential SNES controllers, Nintendo could port over some SNES games to the console too, like Super Mario Kart, Legend of Zelda: Link to the Past and Super Metroid.
There's no word yet from Nintendo on when or even if it plans to actually create the SNES controller, but maybe one day you'll be able play Mario Kart in its full retro glory on the Switch.